Trace analyte detection is the detection of small amounts of analytes, often at nanogram to picogram levels. Trace analyte detection has numerous applications, such as screening individuals and baggage at transportation centers, mail screening, facility security applications, military applications, forensics applications, narcotics detection and identification, cleaning validation, quality control, and raw material identification. Trace analyte detection can be particularly useful for security applications such as screening individuals or items for components in explosive materials, narcotics or biological contaminants where small amounts of these components are deposited on the individual or on the outside of a package or bag.
Trace analysis is also important in pharmaceutical manufacturing. See, e.g. Tan and DeBono, Today's Chemist at Work, November 2004, pp. 15-16 and Munden et al., Pharm. Tech. Eur. Oct. 1, 2002. During the development of a manufacturing process and periodically thereafter, each piece of equipment must be verified, preventing contamination of pharmaceutical ingredient by contact with unclean equipment surfaces. Equipment surfaces are sampled and analyzed for trace contaminants. According to the Food and Drug Administration guidelines chemical residues in manufacturing equipment must be reduced to an acceptable level.
A variety of different techniques can be used for trace analyte detection. These methods include ion mobility spectrometry (IMS), mass spectrometry, gas chromatography, liquid chromatography, and high performance liquid chromatography (HPLC).
IMS is a particularly useful technique for rapid and accurate detection and identification of trace analytes such as narcotics, explosives, and chemical warfare agents. The fundamental design and operation of an ion mobility spetectometer is addressed in, for example, Ion Mobility Spectrometry (G. Eiceman and Z. Karpas, CRC Press, Boca Raton, Fla., 1994). IMS detects and identifies known analytes by detecting a signal which is unique for each analyte. IMS measures the drift time of ions through a fluid, such as clean, dry ambient air at atmospheric pressure. Analysis of analytes in a sample begins with collection of a sample and introduction of the sample into the spectrometer. A sample is heated to transform analyte from solid, liquid or vapor preconcentrated on a particle into a gaseous state. Analyte molecules are ionized in the reaction region of the IMS detector. Ions are then spatially separated in the IMS drift region in accordance to their ion mobility, which is an intrinsic property of an ion. In an IMS detector, where ions carrying a single charge are typically formed, ion mobility is roughly directly proportional to ion mass. An induced current at the collector generates a signature for each ion as a function of the time required for that ion to reach the collector. This signature is used to identify a specific analyte.
A variety of different methods can be used to introduce a sample into a detection instrument and the method will depend, in part, on the type of sample being analyzed and the detection technique. For example, U.S. Pat. Nos. 6,442,997, 6,073,499, 5,859,362, and 5,162,652 disclose devices for collecting vapor or air samples, U.S. Pat. No. 6,073,498 discloses a device for collecting fluid samples, U.S. Pat. No. 5,037,611 is directed to a method adsorbing gaseous samples on a tape, and U.S. Pat. No. 5,741,984 discloses a method which introduces a sample from a finger by pressing the finger on a sampling “token.” U.S. Pat. Nos. 5,859,375 and 5,988,002 are directed to a methods and apparatus for collecting samples using a hand-held sampling device.
Another sampling method involves contacting an object or other substrate to be tested with a fabric sampling swab which collects analyte particles. Upon contact of a sampling swab with a substrate to be tested, solid sample particles can become imbedded into the porous structure of the textile swab. If the sample is in liquid form, the liquid can absorb into the fibers of the swab. In IMS, the swab is placed into the detection instrument and the sample thermally desorbed from the swab. A swab for use in IMS should have absorption and desorption properties suitable for the analytes and substrates to be sampled, should be compatible with the geometry and processes performed by the instrument, should be durable and stable over a range of temperatures, including temperatures in excess of 400° C., and should be substantially free from contaminants and impurities capable in interfering with sample analysis.
A sampling swab should have the ability to absorb and/or adsorb an analyte upon contact with the swab, as well as efficiently desorb the analyte from the swab upon placement of the swab in a detection instrument. For example, a sampling swab should be able to effectively absorb/adsorb volatile substances into its structure or embed sample particles into its porous structure upon contact with an analyte present on the test surface. Additionally, a sampling swab should not interfere with a desorption process of a sample analyte from its surface or fibers during desorption of the collected sample.
A suitable swab also should be durable and stable, capable of resisting chemical and physical decomposition and degradation due to heating and mechanical stress. Decomposition and degradation of a swab can lead to contamination of the detection instrument, thus compromising the integrity of the analysis and potentially fouling the detection instrument. Decomposed and degraded fibers can generate false positives or can interfere with analyte detection resulting in failure in detecting an analyte. In addition, decomposed and degraded fibers can remain in the detection instrument, thus compromising subsequent analyses and risking damage to the detection instrument. The resistance of a swab to decomposition and degradation is affected by physical properties of materials used.
The stability of a textile fiber at high temperatures is particularly important in detection methods involving heating the swab. For example, in ion mobility spectrometry, the swab is heated to desorb and vaporize analyte molecules collected by contact of the swab with a substrate being tested. Thus, it is desirable for the swab to resist decomposition and degradation at temperatures in excess of 400° C. for durations of at least one minute.
It is also desirable that a swab is substantially free of impurities which may interfere with the detection of analytes. These impurities can interfere with the analyte detection by creating unacceptable background signal which swamps out analyte signal and can also cause instrument contamination and instrument failure.
Thus, there is a need for a textile processing and cleaning protocol which results in a swab which is clean and while maintaining sufficient strength and structural integrity.